Method of making an alloy comprising magnesium and thorium



Patented May 11, 1954 METHOD OF MAKING AN "ALLOY COMPRIS- ING MAGNESIUM AND THORIUM William P. Saunders, Midland, Mich., asslgnor to TheDow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application February 27, 1952, Serial No. 273,786

The invention relates to magnesium alloys. It more particularly concerns a method of introducing thorium into melts of magnesium so as to form magnesium alloys containing thorium.

In attempting to produce alloys of magnesium and thorium by the conventional method of reacting a reducible thorium compound with molten magnesium in amount in excess of that corresponding to the stoichiometrical relationship ThF4+2Mg=2MgF2+Th whereby thorium is liberated in situ with the excess of the molten unoxidized magnesium, the difficulty arises that the alloying efficiency is low in that only a relatively small fraction (less than per cent) of the thorium compound becomes alloyed with the unoxidized portion of the magnesium.

It is the principal object of the present invention to provide a method of forming alloys of magnesium with thorium by reacting a reducible thorium compound with molten magnesium whereby the efiiciency of the alloying is increased. Other objects'andadvantages will appear as the description of the invention proceeds:

The invention is predicated upon the discovery that by using thorium tetrafluoride as the source of thorium and forming a melt of it with the chloride of oneor both of the alkali metals potassium and sodium,a composition is obtained which yields magnesium-thorium alloys with increased efficiency of utilization of thethorium on subjectingthe composition to the reducing action of molten magnesium in-a proportion substantially in excess of that corresponding to the aforesaid stoichiometrical relationship as regards the thorium tetrafluoride content of the composition. The invention then consistsof the improved method herein fully described and particularly pointed out in the claims.

In carrying out the invention, for each moleof thorium tetrafluoride used 3 to 7 moles of alkali metal chloride, as either or both potassium chloride :and sodium chloride, are used therewith. One way of'bringingthese materials together to effect a reduction of. the thorium tetrafluoride andbringing aboutalloying of the thorium .liberated in the reduction with magnesium is as fol-. lows: Melt the requisite amount of alkali metal chloride in a suitable vessel, e. g. an iron or steel melting pot, and when the chloride is molten, add with stirring, the requisite amount of thorium tetrafiuoride. The thorium tetrafiuoride rapidly dissolves in the molten alkali metal chloride. The saline melt thus obtained is maintained at a temperature sufiicient to melt magnesium, e. g., 1300 to 1600 F. and. magnesium is added to the 3 Claims. (0]. 75-135) saline melt in excess of the proportions indicated in the foregoing equation as regardsthe ratio of Mg to ThF4. A small. amount,.e. g. 0i5 to 2 per cent of the weight ofthe magnesium, of a conventional magnesium foundry flux is preferably also added to protect the magnesium from attack by the atmosphere while the magnesium is molten and reacting with the ThF4 containing saline melt and becoming alloyed with thorium. The resulting molten mixture is stirred fora short time, e. g., 2 to 20 minutes, during'which the thorium tetrafiuoride becomes reduced and the thorium liberated in the reduction alloys with the magnesium which is present in amount in excess of that required for-the reduction. After stirring the molten mixture, it is allowed to settle for a few minutes, e. g., 5 minutes, and-then the resulting floating metal regulus consisting of a magnesium-thorium alloy may ice-separated from the resulting underlying saline sludge by decantation or otherwise.

The following examples are illustrative of the invention:

EXAMPLE 1 15 pounds of potassium chloride is melted, and, while molten, 20 pounds of solid thorium tetrafluoride is added with stirring. The thorium tetrafiuoride rapidly-dissolves in the molten potassium chloride forming a slightly viscous saline melt containing 3.06 moles of KCl per mole of ThF4. The molten saline melt is poured into a crucible containing pounds of molten magnesium at 1350 F. and the contents of the crucible are stirred for 5 minutes. As the stirring proceeds, the temperature of the resulting mix ture rises to about1400" lit, clue to heat liberation as magnesium reduces the thorium compound-to metallic thorium, a portion of which alloys with the remaining magnesium. Stirring is continued 5 minutes more and then the mixture is left for 15 minutes at 14100 F., whereupon the thorium containing magnesium alloy segregates as a molten metal regulus floating upon a saline sludge. The floating alloy is decanted off and cast into an ingot. ts analysis shows a thorium content of 9.38 per cent. Had all the available thorium become alloyed with all the available magnesium, the resulting ingot would have contained 20.1 per cent of thorium by calculation. The alloying efficiency based upon this calculation is EXAMPLE 2 and 2. The following table sets forth the data 60 pounds of magnesium is melted under the Obtamed' Table Saline Melt Moles Grams Alkali ff Calculated Test No. M Chloride umn Eificiency Grams Grams Alper Mole g of Alloying ThF r311 Chloride ThF4 y 100 71 2.3 6.6 100 71 2. 0a 2. s2 0. 7 100 71 s. 10 9. 30 27. 0 100 71 4. 0s 14. 4 41. 0 100 71 4. as 15. 85 45. o 100 71 5. 94 12. 45 35. 5 100 71 3.14 0.14 17. 5 100 71 11.65 6.93 100 71 4.0 8.89 100 71 Naclflfi} 4.07 13.79 40 *Average of three tests.

protection of 1 pound of a magnesium foundry flux composed of 28 parts by weight of CaCIz, 5'7 parts of KCl, 12.5 parts of BaClz, and 2.5 parts of CaFz. Thorium tetrafiuoride and potassium chloride are fused together in the ratio of 4 moles of K01 per mole of ThF-i. The resulting saline melt is solidified and broken into lumps about the size of a fist. 40 pounds of the lumps of the solidified saline melt of ThF4 and X01 are added to the molten magnesium which is held at about 1400 F. and subjected to stirring for 20 minutes. During the stirring, an additional 5 pounds of magnesium foundry flux is added to protect the magnesium from attack by the atmosphere. The reaction which occurs, liberates thorium from the ThF4KCl composition and a portion of the thorium alloys with the remaining magnesium. The stirred mixture is left for 10 minutes at 1400 F. to stratify. The resulting molten thorium containing magnesium alloy formed floats upon the resulting residue of saline sludge and is then decanted off and cast into an ingot. Its analysis shows a thorium content of 15 per cent. Had all the available thorium become alloyed with all the available magnesium, the resulting ingot would have contained 20.2 per cent of thorium by calculation. The alloying efiflciency based upon this calculation is A series of smaller tests were made which serve to indicate the efiect of the mole ratio of alkali metal chloride to thorium tetrafluoride on the alloying efiiciency. In these tests thorium tetrafluoride was dissolved in melts of alkali metal chloride to form saline melts having various mole ratios of alkali metal chloride to ThFi. Magnesium was then added to the saline melts which were stirred at temperatures of l300 to 1600" F. The resulting mixtures of magnesiumthorium alloy and salines were settled. The alloys obtained were decanted off, cast into in-- gots, and analyzed for thorium. The efficiency of the alloying was calculated as in Examples 1 Referring to the table, it is manifest that the effect of increasing the ratio of the number of moles of alkali metal chloride to the number of moles of thorium tetrafluoride produces a sharp increase in alloying efficiency as the ratio exceeds 3. The efficiency of alloying reaches a peak at a ratio between about 4 and 6 then declines and levels off as the ratio exceeds about 7. A preferred operating ratio is about 4.5.

By the foregoing method, magnesium-thorium alloys containing various amounts of thorium, can be produced with increased efiiciency of thorium utilization. For example, magnesium thorium alloys containing from 0.1 to 35 per cent of thorium or more can be made depending upon the amount of magnesium used relative to the thorium tetrafiuoride. It is preferable to use at least 12 moles of magnesium per mole of thorium tetrafiuoride although proportions as high as 1000 moles of magnesium per mole of thorium tetrafluoride may be used.

I claim:

1. A method of making magnesium alloys containing thorium which comprises subjecting a saline melt of an alkali metal chloride selected from the group consisting of potassium chloride and sodium chloride, said saline melt containing thorium tetrafiuoride in the ratio of between 3 and 7 moles of alkali metal chloride per mole of thorium tetrafluoride, to the reducing action of molten magnesium, the number of moles of magnesium being from 12 to 1000 times the number of moles of thorium tetrafiuoride whereby metallic thorium liberated in the reduction becomes alloyed with magnesium.

2. The method according to claim 1 in which the alkali metal chloride is potassium chloride.

3. The method according to claim 1 in which the alkali metal chloride is sodium chloride.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,648,954 Marden Nov. 15, 1927 2,497,537 Emley et al Feb. 14, 1950 2,604,394 Emley July 22, 1952 

1. A METHOD OF MAKING MAGNESIUM ALLOYS CONTAINING THORIUM WHICH COMPRISES SUBJECTING A SALINE MELT OF AN ALKALI METAL CHLORIDE SELECTED FROM THE GROUP CONSISTING OF POTASSIUM CHLORIDE AND SODIUM CHLORIDE, SAID SALINE MELT CONTAINING THORIUM TETRAFLUORIDE IN THE RATIO OF BETWEEN 3 AND 7 MOLES OF ALKALI METAL CHLORIDE PER MOLE OF THORIUM TETRAFLUORIDE, TO THE REDUCING ACTION OF MOLTEN MAGNESIUM, THE NUMBER OF MOLES OF MAGNESIUM BEING FROM 12 TO 1000 TIMES THE NUMBER OF MOLES OF THORIUM TETRAFLUORIDE WHEREBY METALLIC THORIUM LIBERATED IN THE REDUCTION BECOMES ALLOYED WITH MAGNESIUM. 